(1) The varying number of muscle fibers that contract
<span>In most muscles, the number of muscle fibers in different motor units ranges from a few to hundreds. The nervous system can thus regulate the strength of contraction in a muscle by determining how many motor units are activated at a given instant and by selecting large or small motor unties to activate. </span>
some muscles are almost always partially contracted. In such muscles, the nervous system my alternate activation among the motor units, reducing the length of time any one set of fibers is contracted. Prolonged contraction can result in muscle fatigue due to the depletion of ATP and dissipation of ion gradients required for normal electrical signals.ing.
<span>(2) varying the rate at which muscle fibers are stimulated </span>
<span>single action potential produces a twitch lasting about 100 msec or less. If a second action potential arrives before the muscle fiber has completely relaxed, the two twitches add together, resulting in greater tension. Further summation occurs as the rate of stimulation increases. When the rate is so high that the muscle fiber cannot relax at all between stimuli, the twitches fuse into one smooth, sustained contraction called tetanus.</span>
Explanation:
As the two plates move away from each other in a divergent boundary, the magma from the mantle beneath rises to replace the void created. The magma then cools into a new crust. Before the magma cools, the iron minerals align themselves with the magnetic fields of the earth due to their ferromagnetic properties. These cause the rocks after they are cooled to seem to have bands.
Due to magnetic reversals of the earth's magnetic fields (i.e change in magnetic north and south poles) over several hundred thousand years, these bands will orient differently depending on the then earth magnetic polarity when the magma was cooling.
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Answer: Arctic Ocean
Explanation:
Because the Arctic Ocean is colder it is more dense
